1. Field of the Invention
The invention is primarily directed to ophthalmic wavefront sensing apparatus and methods and more particularly to a wavefront sensor apparatus and method based upon the principles of moiré deflectometry.
2. Description of Related Art
The measurement of wavefront aberrations of the eye up to the 10th Zernike order continues to find increasing application in the field of ophthalmology, particularly in relation to refractive surgical procedures such as LASIK, LASEK, PRK, and others. It is no longer adequate to merely measure the topology of the cornea to determine how to best re-shape a person's cornea for vision correction. And while corneal topography systems used in combination with pachymetry devices and ray-tracing techniques can provide a wealth of information about a person's eye and vision problems, aberrometry provides on its own, unique information about the visual defects of the entire optical system of the eye. Wavefront sensing has application ranging from objective refraction measurement for traditional correction of defocus and astigmatism to contributing to the creation of customized ophthalmic lenses (e.g., contact lenses, IOLs, etc.) and customized laser ablation treatments which have the potential to provide vision improvement up to the theoretical limit of the human eye.
Aberrometers and the principles upon which they operate can generally be classified into four types: (1) out-going (e.g., Hartmann-Shack); (2) double-pass (e.g., slit skioscopy); (3) in-going adjustable (e.g., spatially resolved refractometer); and (4) retinal image aberrometry (e.g., Tscherning, Tracey). In the current commercial environment, Hartmann-Shack wavefront sensor-based aberrometry is most prevalent. However, Hartmann-Shack, as well as the other wavefront measuring principles embodied in the various commercially available devices each have relative identifiable advantages and disadvantages. The interested reader is directed to the Journal of Refractive Surgery, Vol. 16, No. 5 (September/October 2000), which provides a thorough review of ophthalmic aberrometry based upon the proceedings of the First International Congress of Wavefront Sensing and Aberration-Free Refractive Correction.
Ophthalmic wavefront sensing and analysis is by no means limited by the categories described above. Researchers in the field of psychophysics, such as Smirnov in the 1960's, Howland in the mid-80's, and Liang and Williams in the late 80's through the mid-90's, to name just a few, employed various optical principles to acquire and analyze ocular aberration data. Likewise, a great deal of know-how for ophthalmic applications has been transferred from the fields of astronomy, strategic defense initiatives, and optical lens testing.
In International Patent Application Publication WO 92/01417, Horwitz discussed automated binocular vision measurement and correction relying on moiré fringe generation and analysis, commonly known as moiré deflectometry. The publication described a binocular apparatus allegedly having the capability to measure up to 256 aberrations of the eye, and the application of this technology to the design and manufacture of customized ophthalmic lenses and laser refractive surgery. In 1999, Horwitz U.S. Pat. No. 5,963,300 disclosed an ocular biometer based in part upon moiré deflectometry and included a limited teaching of Fourier analysis for providing wavefront aberration information. Notwithstanding the issuance of the '300 patent, it appeared that application of the technology to ocular wavefront sensing needed something more, which apparently was provided, at least in part, by Quiroga et al., Fourier transform method for automatic processing of moiré deflectograms, Opt. Eng. 38(6) 974-982 (June 1999).
The measurement limitations of Hartmann-Shack-type aberrometers and their size, cost, and complexity are issues well appreciated by those skilled in the art. The inventor has recognized that improvements to the apparatus and methods of moiré deflectometry could advantageously address many of the issues associated with current aberrometer technology. Accordingly, the instant specification discloses improved moiré deflectometry apparatus and methods believed by the inventor to provide wavefront measurements having better resolution, higher reliability, and accurate analysis capability that is simpler, less costly, and more robust than Hartmann-Shack and other commercially available ocular aberrometer systems.